The invention concerns an adjustment method, particularly for adjusting optical or fiber optical components, with the features of the preamble of patent claim 1. Moreover, the invention concerns an actuator which is suitable for the same and an optical component.
Laser adjustment methods and actuators suitable for the same have been developed in recent times to enable extremely precise adjustment, e.g., of micromechanical components.
The basic principle of laser adjustment consists of heating a predetermined region of an actuator using a high-energy, preferably pulsed laser beam in a short time, in which the thermal expansion of the relevant region is blocked by corresponding further regions of the actuator. In this manner, compression strains build up in this heated region, which result in a plastic deformation of this region upon reaching the yield point. When this region is cooled down after the high-energy laser beam is switched off, the thermal shrinkage of this region is again essentially prevented by the further regions of the actuator. This leads to the build-up of tensile stresses in the previously heated region which lead to a defined deformation of the actuator, in which the adjustment of a component joined to the actuator is enabled in this process.
The basic principle of such an adjustment method is illustrated in FIG. 1. FIG. 1a shows the starting state of a bar 3 made of a suitable material which is restrained between two rigid demarcations 1. At the starting temperature, e.g., room temperature (20° C.), the bar 3 has a length l0. The center region 3a of the bar 3 is heated by a laser beam 5 in a short time.
This results in the first place in compressive strains σ(−) in the bar 3 since the thermal longitudinal expansion of the bar 3 is blocked by the rigid demarcations 1. In this phase, a negative expansion ε is also customarily defined which corresponds to the compressive strains formed in the bar 3. This phase of the adjustment method is illustrated in FIG. 1b. 
If the compressive strains σ(−) exceed the temperature-dependent yield point σF, a plastic deformation of the bar 3 arises in the region 3a. Correspondingly, the compressive strains in the bar 3 are reduced. This situation is illustrated in FIG. 1c. 
After the laser beam 5 is switched off, the region 3a of the bar 3 begins to cool off, causing a thermal shrinkage of the bar 3. In this process, tensile stresses σ(+) arise in the bar 3 which in actual practice frequently lie in the vicinity of the temperature-dependent yield point σF(T). This situation is represented symbolically in FIG. 1d because seen in the longitudinal direction of the bar 3 whose ends are joined by means of spring elements 7 to the rigid demarcations 1 . . . . [Note: incomplete sentence in the German original]. The spring forces corresponding to the tensile stresses σ(+) cause a defined deformation of the actuator in a practically realized actuator. In this connection, FIG. 1d also shows that the tensile stresses σ(+) arise through the shortening of the bar 3 due to the plastic deformation in the region 3a caused during the heating, in which the length of the bar l1 after the adjustment procedure at the starting temperature is smaller than the original length l0 at the starting temperature.
A problem in the previously known adjustment methods consists in that, as was previously mentioned, the tensile stresses frozen in the bar 3 lie relatively close to the yield point σF. The same can apply also to the compressive strains which occur in those regions which block the thermal expansion or rather the thermal shrinkage of the bar. Since micromechanical or optical components or rather subassemblies in actual practice are always specified for a certain temperature range, e.g., a range from −40° C. to +80° C., and must fulfill predetermined requirements for accuracy and long-term stability within the specified range, there results in previously known adjustment methods a maladjustment of the actuator if the adjusted components or rather the subassembly is brought to a temperature in the upper region of the specified range and the original adjustment was carried out at a significantly lower temperature, such as room temperature. This effect is caused by the temperature dependency of the yield point σF, most materials which are suitable for the manufacture of actuators for laser adjustment methods having a yield point which decreases with increasing temperature. If a temperature is reached at which the yield point σF falls below the value of the frozen-in tensile stresses, this results in a flowing of the material and in a reduction of the tensile stresses to the value of the yield point σF at the relevant temperature. Naturally, this is associated with a corresponding maladjustment of the actuator which is not acceptable at least for components requiring extremely precise adjustment which must be specified over a wide temperature range.